The present invention relates to a method of testing visual fields of the eyes of subjects. More particularly, the invention relates to improvements in a method of examining the visual field of a subject with a perimeter machine, e.g., a machine known as "OCTOPUS" (trademark) distributed by HITRON Corporation, Norwood, N.J.
The automated perimeter machine of HITRON is equipped with a computer and an external memory. A subject who is seated in front of a cupola which defines an illuminated test field is presented a group of stimuli of variable intensity in a sequence which is determined by the computer or by the external memory. The threshold values of the group of stimuli which acted as stimuli to the subject, i.e., which were barely perceived by the subject, are recorded and stored for further reference during the next examination. The first value of each stimulus of the group corresponds to that value which is stored in the external memory. Such first value is normally chosen to correspond to the mean threshold for the respective age group and the selected region of the visual field.
Automatic testing of the visual field normally involves the subdivision of a two-dimensional area into a series of equidistant points which together constitute a lattice or raster. The raster is oriented transversely with reference to a predetermined direction, namely, the direction of gaze. The subject is thereupon presented stimuli at points which are selected at random and the intensity of stimuli is varied, preferably by resorting to the so-called repetitive bracketing strategy (also called staircase or up-and-down method) which leads to greater accuracy in determining the threshold. The threshold value of a stimulus is reached when the subject perceives the stimulus with a 50 percent probability. The reason for starting with a stimulus having a mean threshold for the age group of the subject to be tested is to reduce the number of presentations of stimuli of varying intensity at a given point before the subject perceives the stimulus having the desired threshold value. The aforementioned bracketing strategy also contributes to rapid determination of the threshold values of stimuli for all selected points of the raster.
Automatic programmed perimetry is known for several years. Such automatic mode of perimetric examination enables an ophthalmologist to follow the progress of a disease (or the effectiveness or lack of effectiveness of treatment) on the basis of several tests at regular or irregular intervals, e.g., at intervals of several weeks or months. A drawback of presently known perimetric examination techniques is that the comparison of tests made at timely spaced intervals requires much time and experience. In other words, the task of ascertaining and evaluating differences between the results of successive examinations is a lengthy procedure which must be carried out by a highly skilled physician.
The following prior art publications relate to the field of the present invention: "Octopus-an automated perimeter" (article by J. Spahr and F. Frankhauser in Review of Sensory Disability, No. 18, 1974, pp. 5-8): "Automatisierung der Perimetrie" (article by J. Spahr and F. Frankhauser in Opththalmologica, Basel, No. 170, 1975, pp. 106-107); "Fortschritte in der Automatisierung der Perimetrie" (article by J. Spahr, F. Frankhauser and H. Bebie in Klin. Mbl. Augenheilk., No. 168, 1976, pp. 84-86); U.S. Pat. No. 3,664,732 granted May 23, 1972 to J. R. Lynn.